BRUSSELS — The fast-track ratification of the post-Brexit trade deal between the U.K. and the European Union got underway on Christmas Day as ambassadors from the bloc’s 27 nations started assessing the accord that takes effect in a week.

At Friday’s exceptional meeting, the ambassadors were briefed about the details of the draft treaty by the EU’s chief Brexit negotiator, Michel Barnier. They are set to reconvene again Monday and have informed lawmakers at the European Parliament that they intend to make a decision on the preliminary application of the deal within days.

While voicing their sadness at the rupture with Britain, EU leaders are relieved that the tortuous aftermath of the Brexit vote came to a conclusion in Thursday’s agreement about future trade ties.

All member states are expected to back the agreement, as is the European Parliament, which can give its consent only retrospectively, as it can’t reconvene until 2021. British lawmakers have to give their approval too, and are being summoned next week to vote on the accord.

British Prime Minister Boris Johnson said it gives the U.K. control over its money, borders, laws and fishing grounds. The EU says it protects its single market of 450 million people and contains safeguards to ensure the U.K. does not unfairly undercut the bloc’s standards.

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Johnson hailed the agreement as a “new beginning” for the U.K. in its relationship with its European neighbors. Opposition leaders, even those who are minded to back it because it’s better than a no-deal scenario, said it adds unnecessary costs on businesses and fails to provide a clear framework for the crucial services sector, which accounts for 80% of the British economy.

In a Christmas message, Johnson sought to sell the deal to a weary public after years of Brexit-related wrangling since the U.K. voted narrowly to leave the EU in 2016. Although the U.K. formally left the bloc Jan. 31, it remains in a transition period tied to EU rules until the end of the year.

“I have a small present for anyone who may be looking for something to read in that sleepy post-Christmas lunch moment, and here it is, tidings, glad tidings of great joy, because this is a deal,” Johnson said in his video message.

“A deal to give certainty to business, travelers and all investors in our country from Jan. 1. A deal with our friends and partners in the EU,” he said.

Though tariffs and quotas have been avoided, there will be more red tape as the U.K. leaves the EU’s frictionless single market and customs union. Firms will have to file forms and customs declarations for the first time in years. There will also be different rules on product labeling as well as checks on agricultural products.

Despite those additional costs, many British businesses that export widely across the EU voiced relief that a deal was finally in place, as it avoids the potentially cataclysmic imposition of tariffs.

“While the deal is not fully comprehensive, it at least provides a foundation to build on in future,” said Laura Cohen, chief executive of the British Ceramic Confederation.

PRAISE FOR JOHNSON

An “exceptional victory,” the result of “fantastic work” and a deal that “delivered” for the British people.

Even before the text of the trade agreement was published, lawmakers loyal to Johnson lavished praise on him for resolving an issue that has convulsed British politics for almost half a decade.

When Parliament convenes to ratify the document, the question will only be the size of Johnson’s majority. Even the opposition Labor Party will officially support the deal, arguing that it is better than nothing.

Yet this is unlikely to be the final word in the Conservative bloodletting over Europe that has, at least in part, led to the downfall of the party’s last four prime ministers.

Hard-line Brexit supporters have yet to examine the agreement, and they probably will not like every word of an estimated 2,000 pages of dense treaty text and annexes. A small group did not want any trade deal at all, never really trusted Johnson and might still be inclined to make trouble for him.

Already, an organization representing British trawler fleets has expressed disappointment at compromises over fishing rights, and the Scottish government has attacked the deal, arguing it strengthens the case for Scotland’s independence.

“In the short term, the Tory Party is pretty united around the very hard Brexit that Boris Johnson pushed Britain toward but which many Britons never thought they were voting for,” said Charles Grant, director of the Center for European Reform, a research institute.

But the agreement provides only limited economic benefits for Britain, and friction with the European Union is likely to remain, added Grant, who said the country’s post-Brexit relationship with the European Union may not be much more stable than what preceded it.

“In the longer term, the rift may reopen,” he said, adding that pressure might grow once the deal’s limitations become clear.

The pandemic has plunged Britain into the worst recession in three centuries, so post-Brexit politics remain highly volatile, said Anand Menon, professor of European politics at King’s College, London.

And the Brexit debate has poisoned the workings of the Conservative Party, which had long been known for a pragmatic and successful pursuit of power rather than an adherence to political doctrine.

​​​​​Information for this article was contributed by Raf Casert, Pan Pylas and Angela Charlton of The Associated Press; and by Stephen Castle of The New York Times.